1. Field of the Invention
The present invention relates to a broadcast receiving system to be used when a television broadcast to be received includes character information.
2. Description Of The Related Art
FIG. 2 is a block diagram showing the structure of a prior art broadcast receiving system. This system is made up of a decoder 1 and a television (TV) 2. This TV 2 has a built-in tuner 50 which demodulates an RF receiving signal from the electromagnetic wave broadcast inputted at the input terminal 53 and outputs this to the video processor 51. The demodulated video signal sent from the tuner 50 is then processed by the video processor 51, outputted to the CRT 52 and displayed.
When usual television broadcasts are to be received, the system is just made up of the TV 2. The decoder 1 is connected to the television TV 2, however, in the event of watching a program, for example, on a prescribed scrambled cable television channel.
The decoder 1 also has a built-in tuner 11. This tuner demodulates the transmitted RF signal which has come via cable and outputs the demodulated video signal (detecting signal or intermediate frequency signal(IF signal)) to the descramble circuit 12.
The output from the tuner 11 is also sent to the data extraction circuit 14. The data extraction circuit 14 extracts the key signals necessary for descrambling the scramble signal from the inputted signal and outputs them to the controller 15. The controller 15 then outputs the data corresponding to the inputted key signals to the descramble circuit 12. The scrambled video signal provided by the tuner 11 in accordance with the key signal provided by the controller 15 is then descrambled by the descramble circuit 12.
The descrambled video signal from the descramble circuit 12 is sent to the input terminal 31 of the TV 2 via the multiplexer 13, the output terminal 19 and the cord 21, from where it is inputted to the video processor 51. This inputted video signal is then processed by the video processor 51 and outputted to the CRT 52. In this way, the scrambled video image which was broadcasted can be displayed on the CRT 52 in its unscrambled form.
The decoder 1 also has a circuit set up for displaying predetermined messages (menus) for the viewers (subscribers). This message information is usually transmitted on prescribed cable television channels. i.e. the controller 15 controls the tuner 11 so as to receive electro-magnetic waves for a prescribed channel. The data extraction circuit 14 then extracts the menu information component from the signal outputted by the tuner 11 and outputs it to the controller 15. The controller 15 then controls the character generator 16 in accordance with the information provided by the data extraction circuit 14 and generates character displays for the inputted information.
This display character data is then inputted to the converter 17, converted into, for example, an NTSC video format signal and sent to the multiplexer 13. The multiplexer 13 then superimposes the video signal provided by the descramble circuit 12 with the character display provided by the converter 17. In this way, the video signal on which the character display (menu) has been superimposed can be outputted to the CRT 52 and displayed after having been inputted to and processed by the video processor 51. By doing this, for example, the viewer can select pay per view programs which necessitate special charges as required.
Also, the descramble circuit 12 is controlled by the controller 15 so that a scrambled signal inputted by the tuner 11 will be descrambled and outputted, whereas an unscrambled signal will be outputted without modification.
The decoder 1 also outputs the decoded signal as an RF signal when the television does not have a composite video signal input terminal (in cases where the television only has an RF signal input terminal). i.e. the RF modulation circuit 18 for the decoder 1 modulates the output of the multiplexer 13 and outputs this from the output terminal 20 as an RF signal. This signal is then taken as input at the RF signal input terminal 32 of the TV 2 via the cord 22. The signal inputted via the input terminal 32 is then sent to the tuner 50, demodulated in the same way as for the signal inputted via the input terminal 53, outputted to the CRT 52 and displayed.
The kind of decoder 1 in this prior art broadcast receiving system has a character generator 16 set up for outputting and displaying character information. This both complicates the construction of the system and increases its cost.
As the present invention sets out to solve the above problems, its object is to provide a broadcast receiving system of a less complicated construction at a lower cost.